Tsulong Bug, undeservingly defeated him - What happened?

Hey there! We were doing Tsulong, and we were just getting into it so our DPS/HPS on the boss wasn't optimal. He hit Enrage at 18% HP, kills half of our raid and suddenly drops from 18% to 2% and we won the encounter. I livestreamed this, so here is an archive video.

Looks like rallying cry bugged him out. Rallying cry was applied to your raid (and him) before he transitioned but he didn't gain any health from it, however after he turned to night and it wore off, it actually took health away from him due to how the buff works.

Hey there! We were doing Tsulong, and we were just getting into it so our DPS/HPS on the boss wasn't optimal. He hit Enrage at 18% HP, kills half of our raid and suddenly drops from 18% to 2% and we won the encounter. I livestreamed this, so here is an archive video.

Can confirm this bug and it seems to not just happen if you hit enrage but rather at normal transition. We did the boss yesterday and after we got into the second night phase, the boss dropped incredible low.
But this effect also happens with Ancestral Vigor from Restoration Shamans. Won't be that hard as with Rallying Cry but shall I stop healing now just because of this bug?